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UML™ Bible by Tom Pender

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CHAPTER 11

Modeling an Object's Lifecycle in UML 2.0

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In This Chapter

  • Exploring the change between UML1.4 and UML 2.0 state machines
  • Differentiating simple and composite states
  • Modeling triggers
  • Defining and modeling transition types
  • Working with regions – entry and exit, join, junction, choice and history pseudo states
  • Defining and modeling submachines
  • Defining and modeling protocol state machines

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The single greatest change between UML 1.4 and 2.0 state diagrams (apart from the ongoing name changes) is the effort to separate the semantics of the Activity diagram from that of the state machine semantics. In UML 1.4 there was an attempt to treat the Activity diagram as a subset of the state machine semantics. This resulted in a kind of forced fit that limited the features of the Activity diagram and drew attention away from some of the features that could be valuable in a state machine, such as deferred events, the description of the logic of transitions in terms of sending and receiving signals, and making decisions during the transition. UML 2.0 draws a clear distinction between the semantics of the two types of diagrams and remedies many of these artificially imposed limitations.

The expression “state machine” is used with three different meanings in the UML 1.4 and 2.0 specifications. ...

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